"One Nation Under God." That line, enshrined in the American Pledge of Allegiance, is the theme selected by a self-appointed "task force" that seeks to set an agenda for Thursday prayer events around the country.

But if you were expecting this day to be all about quiet reverence and heartfelt petition, well, just remember that this is an election year, and that religion is a topic that sometimes generates a wee bit of controversy in the public square.

Yes, legions of Americans including Marines in Georgia and residents of Colorado Springs are gathering to pray, whether led by pastors or kneeling in silence among church pews.

The other reality of this day, however, is that it has become an annual part of the political fabric. It's a day when politicians appeal to voters as people of faith, when interest groups cast wary judgment on politicians, and when many atheists and civil libertarians seek to cast doubt on the very concept and constitutionality of an annual day for prayer in the US.

Start with the fact that it's the president who proclaims the National Day of Prayer (following a 1952 law), but the task force publicizing the "One Nation Under God" theme – the National Day of Prayer Task Force – is headed by the wife of James Dobson, founder of Focus on the Family and a leader in the evangelical Christian movement.

The White House lists the president's schedule for May 3 as including a lunch with the vice president, a meeting with senior aides, and some remarks at a Cinco de Mayo Reception in the Rose Garden. (An aside: Is that odd, to be celebrating Cinco de Mayo two days early? Just curious.)

The president's proclamation included an exhortation to pray for members of America's armed forces, and for "those who are sick, mourning, or without hope," and to "ask God for the sustenance to meet the challenges we face as a Nation."

Mitt Romney, poised to become the Republican nominee for president, released his own statement of prayer. “Today I join with people of all faiths to express devotion and gratitude to the Lord, who has so richly blessed us," he said. His concluding phrase appeared to be a nod to the task force evangelicals, calling on "the Lord [to] keep us strong and free and we will remain one nation under God."

A year ago, a federal appeals court overturned a ruling that the National Day of Prayer was unconstitutional.

Mr. Obama took an effort to be inclusive of the many views Americans have on religion, saying that the nation's democracy "respects the beliefs and protects the religious freedom of all people to pray, worship, or abstain according to the dictates of their conscience."

At the same time, some critics say the Obama administration hasn't stood up strongly enough for religious freedom.

The Catholic News Agency, for example, quotes legal expert Robert Tyler of Advocates for Faith and Freedom, raising questions about Obama's statement supporting a "democracy that respects the beliefs and protects the religious freedom of all people to pray, worship, or abstain....” Mr. Tyler said this could be understood as supporting freedom of worship but not freedom to fully to practice a religion.

That distinction came up, in the context of the Roman Catholic faith, when the Obama administration issued a mandate that employer health insurance cover contraceptive services.

The idea of an annual day of prayer was enshrined in law under President Truman (D) in 1952, and President Reagan (R) signed a 1988 law calling for the event to be held on the first Thursday of each May.

Prior to that, leaders including the Continental Congress and Abraham Lincoln on occasion proclaimed days of prayer for specific reasons.